TRANSIENT COMPARTMENTAL EXPRESSION OF A FAMILY OF PROTEIN-TYROSINE PHOSPHATASES IN THE DEVELOPING STRIATUM

The expression of a family of intracellular protein tyrosine phosphata ses (STEP) was studied in the striatum of rats during ontogeny. Links between the formation of dopamine islands and STEP immunoreactive patc hes in the striatum were examined since previous work had suggested th at STEP isoforms were selectively expressed in dopaminoceptive brain r egions. STEP protein and mRNAs were distributed in a patchy manner dur ing the first postnatal week. By 2 weeks, STEP immunoreactivity was ho mogeneous, indicating that both patch and matrix neurons express STEP by maturity. Two-color immunofluorescent staining was also performed t o compare STEP with specific markers for patch and matrix. Tyrosine hy droxylase immunoreactive fibers from the substantia nigra form distinc tive dopamine islands in the striatum during late embryonic developmen t, and occupy the sites of future patches [23,37,38,54]. These fiber i slands align with STEP immunoreactive neuronal patches during the firs t two postnatal weeks, suggesting that STEP is a marker for patch neur ons in early postnatal development. When STEP's distribution was compa red with other markers for patch (substance P) or matrix (calbindin), STEP co-localized with substance P in most striatal neurons on postnat al days 1 through 7. However, STEP was also expressed within a subset of calbindin-positive neurons in the lateral striatum, but not with th ese neurons elsewhere in the striatum. By adulthood, STEP colocalized with both markers. These results suggest that STEP is expressed first within patch neurons but not matrix, and subsequently within both. The expression of STEP may be triggered by the arrival of striatal affere nts or other regulatory factors.